World leaders expressed shock and horror after a gunman massacred 20 small children and six teachers Friday in the US state of Connecticut, in one of the worst school shootings in history.

"I would like to express my shock at the tragic shooting at the school in Connecticut
today," European Union diplomacy chief Catherine Ashton said

The head of the European Commission Jose Manuel Barroso spoke of his "deep shock and horror" upon hearing of the massacre at Sandy Hook Elementary School, which he called a "terrible tragedy".

"Young lives full of hope have been destroyed," he said in a statement.

Local media said that the shooter, reported to be a young man who picked off his victims with unusual accuracy, began in the kindergarten section where he killed his teacher mother and her class, then moved on.?

The child victims were reported to be aged between five and ten.

"I was shocked and deeply saddened to hear about today's horrific shooting," British Prime Minister David Cameron said.

"My thoughts are with the injured and those who have lost loved ones. It is heartbreaking to think of those who have had their children robbed from them at such a young age, when they had so much life ahead of them."

Britain's Queen Elizabeth II sent a message to President Barack Obama in which she said she was "deeply shocked and saddened" to hear of the shootings.

"The thoughts and prayers of everyone in the United Kingdom and throughout the Commonwealth are with the families and friends of those killed and with all those who have been affected by today's events."

French President Francois Hollande also extended his condolences to the victims and their relatives in a message to Obama.